Electron discharge device



Feb. 22, 1949. J. H. FREMLIN ETAL 'ELECTRON DISCHARGE DEVICE Filed March 26, 1945 2 Sheets-Sheet 1 Inventor. f .amm Heaven 'FRENLm Feb- 22, 1949i J. H. FREMLIN ETAL ELECTRON DISCHARGE DEVICE 2 sheets-sheet 2 'Filed March 26, 1945 1 nventor 0mm HEswER T REMUN Patented Feb. 22, 1949 UNITED STATES RATENT ELECTRON DISCHARGE DEVICE Application -ll/iarclrZ, 1945, Serial No. 584,818 ln Great Britain @December 6, 1943 or-FICE Section 1, Public Law 690, August 8, 1946 Patent expires December 6,l 1963 The present invention relates to electric discharge devices of the electron velocity modulation type, and is concerned with tuning arrangements for the resonators of such devices, par' 2 Claims. (Cl. 315-5) the electronV velocity modulation. type adapted to generate oscillations of a given frequency, which includes constructing a hollow resonator for Vthe said `generator adapted to resonate slightly above ticularly for oscillation generators. 5 the given frequency, screwing a screw through vIn radio communication systems, it is common the wall of the resonator, supplying oscillations practice to employ superheterodyne receiving at the given frequency to excite the resonator, circuits in which the local oscillator may have to 'connecting the resonator to a wave detector, and be tuned over a relatively wide range. Such tunadjusting the screw to vary the portion extending is sometimes accomplished by. a mechanical in ing inside the resonator until the detector indiarrangement adjustable by hand, but when the -c'ates maximum excitation of the resonator, the frequency of the received waves varies rapidly, said operations being carried vout before asseman automatic frequency control arrangement is bling the resonator inside an enclosing envelope. necessary for keeping the oscillator in tune. De- The invention will be explained with reference vices are known in which' the tuning is effected l5 to the accompanying drawing in which: electrically by varying the velocity of the elec- Fig. 1 shows a perspective View, vpartly cut tron beam, and these are particularly suitable away, of a co-axlal line resonator for a device for the application of automatic frequency conaccording to the invention; trol. However, at very short wave lengths it A Figs. 2 and 3 show sectional views of two albecomes diicult to make the resonators with a to ternative forms 4of the invention; sufficient degree of precision to ensure that the Fig. 4 shows diagrammatically a test arrangemean frequency generated by the device is within ment used in the adjustment of the resonance the necessary limits. Suppose, for example, that frequency ofthe resonator; and the mean frequency to be received is 3,000 mega- Fig.. 5 shows a. perspective diagrammatic view cycles per second, and that this frequency may ci the complete device with the envelope revary by i1%, or m30 megacycles per second. A moved, and with parts cut away to show details. suitable generating device may be electronically Fig. 6 shows a cross-sectional view of the detunable over a range of i35 megacycles and it vice of Fig. 5 assembled in its envelope along the will be .evident that its mean frequency must be lines of the beam path. within the limits 3,000i5 megacycles, on the as- 30 In order to illustrate the invention,A an elecsumption that the resulting intermediate fretron velocity modulation type oscillator comquency is small compared with the incoming freprising a co-axial line resonator will be described. quency, This requires an accuracy of 5 parts Such va device may be ofthe kind described in in 3,000, and resonators cannot be made to fulthe specification of Patent No. 2,320,860. Fig. 5 l such a requirement without the use of most 35 gives a diagrammatic View of thedevice and expensive tools. However, an accuracy of i2% Fig. 6 .gives a cross-sectional view. The co-axial can be easily achieved without specially accurate resonator is shown at I4, and an electron beam tools, and it is the principal object of the presis fired through a slot 2y therein from a gun ent invention to provide a simple means to enable diagrammatcally Shown as consisting of a, cathsuch resonators to be adjusted during manufac- 40 ode I5 and 001117101 electrode 46,v and is collected ture so that the desired accuracy of the mean by a plate i1. The disc .IB is secured to the wall generated frequency is obtained, so that no exlof theresonator vIlland is sealed throughY the ternal trimming condenser or the like needs to .envelope 20 of .the device, which envelope `is be supplied. shown in Fig. 6. Fig. l shows part ofthe re's- According to the invention, an electric dis- "15 onator I4 to an enlarged scale to Vshowufthe feacharge device of the electron velocity modulatures of the invention clearly. I is the cylindrical tion type comprises a system of one or more holwall lof the resonator I4,l and 2 is one end of low resonators adapted to be excited by a beam the slot through which they electron beam is proof electrons projected therethrough, a screw bejected. The passage for the beam is vdeiined by ing provided through the wall .of a resonator and 50 parallel fins 3 attached to the wall I, and by the extending thereinto for the purpose of adjusting parallel fins Il attached to the central conductor the resonance frequency of the resonator by ad- I 9 of the co-axial resonator III,` seen only in justment 0f the screw Fig. 5. rIf'hese arrangements are all quiteconven- The invention also comprises a method of mantional and are explained in the above mentioned ufacturing an electric oscillation generator of 35 specification.

4this is often unnecessary "as already explained.

According to the invention, a screw 5 is screwed through the wall I and extends into the resonator in a region where the electric field is strong, and by adjustment of the screw from outside, the length which projects inside may be varied, thereby changing the resonance frequency of the resonator. The screw may be considered as distorting the electric eld inside the resonator, or alternatively it may be thought of as introducing a variable capacity between the end of the screw and the adjacent n 4, which capacity loads the end of the resonator, and therefore affects its resonance frequency.

If the wall of the resonator is too thin to provide a satisfactory support for the screw 5, a suitable nut or washer 6 may be brazed, or soldered, or otherwise secured to the outside surface of the wall I as shown in Fig. 2. Alternatively, a hole may be punched inwards as shown in Fig. 3 to provide lbearing surfaces 1 into which suitable threads may be tapped to accommodate the screw.

When the position of the screw has been adjusted in the manner which will be described later, it is usually desirable that it should be rigidly xed or otherwise sealed in order to prevent any subsequent alteration. This may be conveniently done by winding a turn of metallic tin wire or other solder round the screw where it joins the outside of the wall or washer 6; this wire will melt during the subsequent processing of the device and will secure the screw rmly in place. The arrangement shown in Fig. 3 is particularly suitable for this process, since the recess at 8 forms a convenient receptacle for the melted tin or solder, and a very neat and satisfactory joint results. The sealing or xing material could alternatively be a cement or the like of any type suitable for use in a vacuum tube.

One method of setting the adjustment of the screw 5 is shown diagrammatically in Fig. 4. The assembly of the device is completed up to the point just before it is to be sealed into its envelope. Only the upper part of the resonator I4 is shown in Fig. 4, and it will be designed for a resonance frequency perhaps 2% above the final desired value, when the screw 5 is fully withdrawn from the inside of the resonator. The resonance frequency of different samples will thus be expected to vary over the range to 4% above the final desired value. A co-axial transmission line 9 is connected by an adapter I0 to the open end of the resonator, and is connected at its other end to a generator, not shown, supplying oscillations at a frequency higher than the desired final res onance frequency by an amount equal to the frequency drift which occurs in the finished device during the warming up period. The inner conductor of the co-axial line 9 terminates in a short probe I I for the purpose of exciting the resonator. A small hole I2 is provided in the wall I of the resonator IlI opposite the screw for transferring the oscillations to a crystal detector unit I3 tuned to the generator frequency. -The screw 5 is adjusted until a maximum reading is obtained on a suitable indicator, not shown, connected to the crystal detector. Then the resonance frequency of the resonator is closely equal to the desired value. The hole I2 may finally be closed, though if the hole is small, and the device is assembled inside its envelope and the usual pumping and processing operations are performed. During the heating for out-gassing the device, the screw 5 becomes soldered in place The resonator should, of course, be properly annealed before the adjustment is made, otherwise distortion is likely to take place during the' subsequent processing.

The most suitable size of the screw 5 depends on a number of factors, such as the equivalent capacity of the resonator, the mean resonance frequency, and the desired range of adjustment. The total range available should be rather greater than is actually necessary, because adjustment becomes very critical if the end of the screw gets too close to the iin 4. In a particular case where the wave-length was 10 cm. and a range of adjustment of 5% was desired, a standard 6 BA screw was found to be suitable.

It will :be evident that although a device with a co-axial resonator has been illustrated, a similar screw arrangement could be used to adjust other types of resonators employed in electron velocity modulation devices, which are not necessarily oscillation generators. For example, in devices of the type employing two separate resonators with a drift tube between, each of the said resonators could be provided with a screw through the wall projecting into a strong part of the field, for adjusting the resonance frequency.

What is claimed is:

1. An electric discharge device of the electron velocity modulation type comprising a hollow resonator of the coaxial line type having an open end and a, closed end, means adjacent said resonator for projecting a beam of electrons through said resonator for exciting said resonator, and a. single adjustable screw screwed through the outer line at a point adjacent said open end of said coaxial line type resonator and having a portion adapted to extend into the interior towards the inner conductor thereof whereby the resonator is tuned to a desired fr-equency.

2. A method of manufacturing an electric oscillation generator of the electron velocity modulation type adapted. to generate oscillations of a given frequency which includes constructing a hollow resonator of the coaxial-line-type for the said generator adapted to resonate slightly above the given frequency, screwing a screw through the outer line of said resonator, locating fusible material in the neighborhood of the joint between the screw and the outer line, supplying oscillations at the given frequency to excite the resonator, connecting the resonator to a wave detector, adjusting the screw to vary the portion extending inside the resonator towards the interior line thereof until the detector indicates maximum excitation of the resonator, assembling the resonator in an enclosing envelope, and heating the resonator to melt the fusible material for the purpose of sealing the joint.

JOHN HEAVER FREMLIN. lSTANLEY GORDON TOMLIN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,167,201 Dallenbach July 25, 1939 2,338,306 Smyth Jan. 4, 1944 2,356,414 Linder Aug. 22, 1944 2,389,271 Mouromtsei et al. Nov. 20, 1945 Gurewitsch Nov. 19, 1.946 

